Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing liquid or solid sample
Reexamination Certificate
1999-10-04
2001-08-21
Snay, Jeffrey (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing liquid or solid sample
C422S082090, C356S329000
Reexamination Certificate
active
06277330
ABSTRACT:
The present invention relates generally to an optical sensor and more particularly to an optical sensor which utilizes a polymer thin film for directly detecting a chemical substance dissolved or dispersed in water, particularly dissolved organic carbon (hereinafter abbreviated as “DOC”) in accordance with an optical detecting method such as a waveguide mode method (WG method), surface plasma resonance method (SPR method), interference enhanced reflection method (IER method), and so on. The polymer thin film interacts with a chemical substance such as hydrocarbon and so on which may be absorbed into or adsorbed on the polymer thin film. As a result, the polymer thin film exhibits a change in thickness and/or refractive index depending on the concentration of the chemical substance, so that such a physical change may be measured by an optical method to determine the concentration of the chemical substance dissolved or dispersed in water, particularly, DOC.
A variety of reports have been made on the use of polymer thin films in optical sensors for detecting chemical species in gas phase and chemical substances dissolved in water. Many of these reports are related to fiber optic sensors or optical waveguide sensors based on evanescent waves or guided waves.
As is well known in the art, when a light beam is incident on an interface between two dielectric materials having different refractive indices n
1
and n
2
(>n
1
), respectively, total internal reflection occurs when the light beam is incident from the dielectric material of the refractive index n
1
to the dielectric material of the refractive index n
2
and when the angle of incidence is larger than a critical angle &thgr;c. The critical angle &thgr;c of total internal reflection is given by:
&thgr;c=sin
−1
(n
1
2
) (1)
In this case, the incident light is fully reflected back into the dielectric material of the refractive index n
2
so that no light will enter the dielectric material of refractive index n
1
. However, there exists a wave function called an evanescent wave which propagates in parallel with the interface between the dielectric material of refractive index n
1
and the dielectric material of the refractive index n
2
. The electric field E of the evanescent wave decays exponentially with the distance
z
from the interface, and can be expressed by an exponential function:
E=E
0
exp(−z/d
p
) (2)
where E
0
is the electric field on the interface, and d
p
is the depth of penetration defined as the distance where the electric field of the evanescent wave, produced when light is incident on the interface at an angle &thgr;, is reduced from the value at the interface to 1/e, and is expressed by:
d
p
=&lgr;[2&pgr;(n
2
2
sin
2
&thgr;−n
1
2
)
½
] (3)
As is well known in the art, optical waveguides operate based on the principle of total internal reflection. A planar waveguide, which is one type of the optical waveguides, simply consists of a first medium of refractive index n
2
sandwiched between a second medium of refractive index n
1
and a third medium of refractive index n
3
, where the refractive indices of the media are selected such that n
2
>n
3
≧n
1
is satisfied. A light beam is confined in the first medium by successive total reflections when the light beam is traveling in the medium n
2
at an angle &thgr; larger than the critical angle of total internal reflection on interfaces of the first medium and the two other media (in this event, sin &thgr;>n
3
2
≧n
1
2
is satisfied). In this case, waveguiding occurs, and the light waves existing in the first medium are called guided waves. Optical fibers are another type of waveguides consisting of a cylindrical core of refractive index n
2
surrounded by a cladding layer of refractive index n
1
(<n
2
).
In either evanescent wave sensors or guided wave sensors, light must travel at an angle larger than the critical angle of total internal reflection. Typical examples of optical chemical sensors based on evanescent waves can be found in many prior art documents. Carter et al. disclose in USP No. Re.33064 a method of identifying a chemical species in a solvent using an optical waveguide covered with a response film having a refractive index smaller than that of the waveguide layer. Light propagates through the optical waveguide by the action of total internal reflection.
Within the propagating light, evanescent waves generated by the total reflection only are involved in interaction of the response film with a chemical species under detection. Thus, the method proposed by Carter et al. is limited only on interaction which is accompanied with absorption or scattering of light, or generation of fluorescence.
Hinrich et al. have reported the use of polymer for detecting organic compounds in water on an internal reflection element in “Determination of organic compounds by IR/ATR spectroscopy with polymer-coated internal reflection elements” (Applied Spectroscopy, Vol. 44, No. 10, 1990, pp 1641-1646). However, the detecting method of Hinrich et al. relies on the absorption of evanescent waves of infrared rays penetrating in the polymer film by organic compounds, wherein the polymer film is used to eliminate water and extract the organic compounds on the surface of the internal reflection element to thereby enhance an absorption signal.
Burck et al. have reported a similar method except for the use of an optical fiber in “A fiber optic evanescent field absorption sensor for monitoring organic contamination in water” (Fresenius J. Anal. Chem., (1994), 342, pp 394-400) and “Fiber-optic evanescent wave sensor for in situ determination of non-polar organic compounds in water” (Sensors and Actuators, B 18-19 (1994), pp 291-295).
Japanese Laid-open Patent Application No. 7-85122 (1995) discloses a method for detecting an organic solvent in water with an optical fiber having a cladding layer made of a chitosan compound. Since the intensity of evanescent waves penetrating into the chitosan cladding layer depends on the degree of swelling, and the concentration of the chitosan cladding layer varies in accordance with the ratio of water to solvent, the intensity of light propagating the optical fiber is consequently a function of the concentration of organic solvent dissolved in water.
A main disadvantage of a sensor utilizing evanescent waves, however, is that the sensitivity of the sensor is limited since only a portion of incident light is used for detection. Thus, a long interaction distance is required to realize a sensor having a high sensitivity. This imposes a limit on reduction in size of such sensors.
A larger portion of incident light may be utilized for detection to provide sensors having higher sensitivities. WO95/20151 discloses a chemical sensor having a multi-layered optical fiber. Specifically, a sensing polymer layer is sandwiched between a core of the optical fiber and a cladding layer, and the refractive index of the polymer layer is larger than that of the cladding layer so that the polymer layer serves as an optical waveguide layer. With this structure, light incident to the optical fiber is refracted toward the polymer waveguide layer and propagates therethrough toward the end terminal of the sensor. However, since this structure requires an output light detector to be located near an output terminal, the chemical sensor disclosed in WO95/20151 is inconvenient for measuring a substance to be detected in water.
A large number of highly sensitive polymers for detecting chemical substances in gas have also been reported. Gliliani et al. have reported a strip-shaped polymer waveguide having a thickness of 1 &mgr;m for detecting the existence of several kinds of organic vapors in “Fabrication of an integrated optical waveguide chemical vapor microsensor by photopolymerization of a bifunctional oligomer” (Appl. Phys. Lett., 48 (1986), pp 1311-1313) and “Integrated optical chemical vapor microsensor” (Sensors and Actuators, 15 (1988), pp 25-31).
Liu Yuan
Tagaya Akihiro
Yamamoto Hironobu
Aventis Research & Technologies GmbH & Co K.G.
Connolly Bove & Lodge & Hutz LLP
Snay Jeffrey
LandOfFree
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